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Conditions of the consent require restoration of the pipi beds, creation of an artificial reef and careful placement of the dredged sand in approved locations.

A new trust, with members from local iwi, the port and other stakeholders, is also to be set up.

Mr Cairns said the company would soon begin preliminary stages of the dredging process, expected to continue through the year.

The first stage would cost between $30 million and $40 million and was likely to take six months to a year to complete, depending on the size of the dredger.

The second stage would increase the depth of the channel by 3.3 metres and remove 32 metres of Tanea Shelf to make the channel wider.

Dr Smith said he was "disappointed" it had taken nearly four years for a final decision.

The case was one of the last being dealt with under the old Resource Management Act. Future consents of this type would be determined by the Environmental Protection Authority, rather than the minister, and within nine months, he said.